[The Rudolf Virchow Prize 2001. The role of the oncoprotein beta-catenin ni the progression of colorectal cancers].

Invasion and dissemination of well-differentiated carcinomas are often associated with loss of epithelial differentiation and gain of mesenchymal-like capabilities of dedifferentiated tumor cells at the invasive front. However when analysing central areas of metastases of colorectal carcinomas one finds a regain of the differentiated epithelial growth patterns like in the primary tumor. More than 80% of these tumor have loss of function mutations in the APC tumor suppressor gene, leading to an overexpression of beta-catenine. In its nuclear pool beta-catenine acts as a transcription factor and is now considered as one of the main oncogenic proteins in colorectal carcinogenesis. We could define several molecules important for the processes of invasion and dissemination, like MMP-7, uPA, laminin-5, as target genes activated by nuclear beta-catenine. Moreover the characteristic phenotypic changes during tumor progression were associated with distinct expression patterns of beta-catenine and E-cadherin. Nuclear beta-catenine was found in dedifferentiated mesenchyme-like tumor cells at the invasive front, but strikingly, like in central areas of the primary tumors, was localized to the membrane and cytoplasm in polarized epithelial tumor cells in the metastases. This was accompanied by changes in the proliferative activity. Based on these data, we postulate that an important driving force for progression of well-differentiated colorectal carcinomas is the specific environment, initiating two transient phenotypic transition processes by modulating intracellular beta-catenine distribution in the tumor cells.